Electrical circuits



Oct. 10, 1933. J. B. DOW 1,929,413

ELECTRICAL C IRCUITS Filed July 51, 1929 INVEN TOR. Jemzz'r a 5. flow BYMW A TTORNEYS.

Patented Oct. 10, 1933 UNITED STATES PATENT oFF cE 4 Claims.

(Granted; under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757') My invention relates broadly to electric circuits and more particularly to selective circuits to be used in radio receiving apparatus.

The object of my invention is to produce a special amplifying filter circuit of high selectivity, low resistance losses and one which will prevent radiation of signals upon the antenna circuit should the-filter circuit be used before a regenerative detector which is oscillating at a frequency slightly different from the incoming signal or should the filter circuit be used before some other receiver in which oscillations are produced for heterodyne purposes.

Further objects of my invention will appear more fully hereinafter as the description of the method and apparatus is developed.

It has long been recognized that the use of intermediate circuits between the detector and the antenna system of a radio receiver results in a gain in selectivity thereby making the receiver less subject to interfering disturbances. However, in the use of the-ordinary tuned intermediate circuits the improvement is not as great as might be accomplished because of the r decrease in signal strength due to the added effective resistance of the intermediate circuits.

I have developed a regenerative filter circuit hereinafter referred to as my improved amplifier circuit in which not only is the resistance of a very low value but also the possibility of radiation into a the antenna system from an oscillating detector is prevented; a thing which is not accomplished by the use of the ordinary intermediate stages of tuned circuits because the resonance curves of such circuits do not show a suflicient sharpness to prevent such radiation.

My invention consists substantially in the construction, combination and arrangement of parts associated therewith or as will be more fully hereinafter set forth as shown by the accompanying drawing and finally pointed out in the appended claims.

Reference is to be had to the accompanying drawing which diagrammatically represents an oscillating detector coupled to an antenna circuit through one stage of my improved amplifier circuit. This circuit may be used before a regenerative or other non-oscillating detector should selectivity with respect to external interference be paramount.

The numeral 1 designates any conventional type antenna to the inductance 2 of which is coupled a coupling coil 3. The coupling coil 3 conveys the signals received upon the antenna 1 through a shield 4 to the main inductance of the resonant circuit of the first stage of my improved amplifier circuit.

The resonant circuit consists of amain inductance 5, the coupling coil 3, a variable condenser 6, and a'second coupling coil or interstage coupling coil 7; Connected to the main inductance of the resonant circuit is a vacuum tube 8, the filament 9 of which is supplied with a heating current from a source of power 10. One terminal of the filament is connected to the point 11 of the main inductance 5 and is grounded to the partition 11 of the shield 4. The plate 12 of v the vacuum tube 8 is connected through a source of plate current supply to a variable. tap 13 near I to a variable tap 15 which makes contact with the v several turns of the main inductance 5 on the opposite side of the grounded point 11 of the main inductance 5 from the variable tap '13 of the plate filament circuit of the vacuum tube.

The coupling coil 7 is led through the partition 11 of the shield and is coupled to the input coil 16 of the detector circuit. For purposes of simplifying the drawing, I have indicated the use of ordinary inductive coupling to both the antenna and detector circuits. It will be understood, however, that any of the well known methods of coupling may be employed. It is to be understood that any type of detector may be used; but, for the purpose of illustration, I have shown a vacuum tube 17 the filament 18 of which is supplied with heating current from a source of power 19, one terminal of which is grounded to the shield 4. I V

The grid 20 of the vacuum tube 1'7 is connected I to the grounded filament terminal 21 through a grid condenser and grid leak 22, and the input coil 16, in parallel with which is a variable tuning condenser 23. a e

The plate 24 of the vacuum tube 17 is connected through a regenerative coil 25, an indicator 26, and a source of plate current supply 2'7, to the grounded terminal 21 of thefilament. The indicator 26 is shunted by a condenser 28 which serves as a by-pass for the high frequency currents. k

When the detector is made to oscillate by the close proximity of the coil 25 to the coil 16 and the variable taps 13 and 15 are so adjusted that the amplifier circuit is just below the oscillating point, the system will not radiate signals from the antenna 1, which originates in the oscillating detector. It is understood that the usual condition exists wherein the detector is oscillating at a frequency slightly difierent from that which it is desired to receive. Regeneration in the units of the main inductance 5 between'the points 15, 11 and 13 maintain the efiective resistance of the amplifier circuit at a very low value. Any other of the many circuits for producing and controlling regeneration in a tuned circuit may be used. In this manner I have produced a regenerative filter circuit which is not only very selec-- tive, but also one which is very efficient due to its very low effective resistance and regenerative properties and the extremely loose coupling required between the coils 2 and 3 and the coils 7 and 16; and one which will not radiate from the antenna 1 signals which would otherwise originate in the oscillating detector.

While I have disclosed my invention in one of its preferred embodiments, I desire it to be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the'scope of the appended claims.

The invention described herein'may be manufactured and used by the Government of the United States for governmental purposes without the payment to me of any royalty thereon.

Having thus described my invention, what I claim is as follows: p

1. In combination with a regenerative vacuum tube detector and an antenna, a regenerative radio frequency amplifier, said amplifier consisting of a coupling coil coupled to the antenna, a coupling coil coupled to the regenerative detector and a main inductance between the coupling coils and means for tuning the inductance to the frequency of the signals received, by the antenna and a vacuum tube, the electrodes. of which are conradio frequency amplifier, said amplifierrconsisting of a coupling coil coupled to the antenna, a coupling coil coupled to the regenerative detector and a main inductance between the coupling coils and means for tuning the inductance to the frequency of the signals received by the antenna and a vacuum tube, the electrodes of which are coupled to the main inductance, the filament of the vacuum tube amplifier connected to a point intermediate to the ends of the main inductance and means for connecting the plate and grid of the vacuum tube to points along themain inductance upon opposite sides of the point at which the filament is connected to the main inductance.

3. In combination with a vacuum tube detector and'an antenna, a regenerative radio frequency amplifier, said amplifier consisting of a coupling coil coupled to the antenna, a coupling coil coupled to the detector and a main inductance between the coupling coils and means for tuning the inductance to the frequency of the signals received by the antenna and a vacuum tube, the electrodes of whichare coupled to the main inductance, the filament ofthevacuum tube amplifier connected to a point intermediate to the ends of the main inductance and means for connecting the plateiand grid of the vacuum tube topoints along the main inductance.

4'. Incombination with a vacuum tube detector and an antenna; a regenerative radio frequency amplifier, said amplifier consisting of a coupling coil coupled tothe antenna, a coupling coil coupled to the detector and a main inductance between the coupling coils and means for tuning The inductance to the frequency of the signals received by'the antenna and a vacuum tube, the electrodes of which are coupled to the main inductance,-the filament of thevacuum-tube amplifier connected toa point intermediate to the ends the main inductanceand means for connecting the plateand grid of the vacuum tube to points along the -main inductance upon opposite sides of the point at which the filament is connected to the main inductance. v p

- JENNINGS B. DOW. 

